Pumping systems having a reciprocating movement for permitting the upstrokes and downstrokes of the pumps have been known for a long time. The great majority of those pumping systems use a combination of a piston having a short length and a corresponding traveling valve. Such a piston travels within a cylindrical body, a so-called barrel, having a considerable length relative to the piston. A fixed valve is located at the lower extremity of the barrel.
It is understood that such traveling and fixed valves are required in the downstroke phase, to enable the chamber of the piston being filled with the fluid being extracted and, in the upstroke phase, to lift the fluid with the piston.
Often, the fluid being extracted contains sand, drillings or other abrasive solids. The solids can become lodged in the annulus between the external wall of the piston and the internal surface of the barrel, thereby displacing the piston relative to the barrel. The solids are then drawn along the length of the stroke of the piston. In view of the pressure of the column of fluid being extracted, for example at 200 kg/cm2, the solids can cause wear through abrasion. Moreover, the piston may even lock or seize against the barrel, thereby requiring the fluid extraction operation to be stopped.